The present invention relates to an electroluminescence element, which will be referred to as xe2x80x9can organic EL elementxe2x80x9d in this specification hereinafter, used as an element of an organic electroluminescence display. More particularly, the present invention relates to an organic EL element and a manufacturing method thereof in which patterning can be easily conducted when an organic thin film is laminated on an anode and a cathode is formed on the organic thin film.
The organic EL element is used for a back light of a liquid crystal display, a display applied to various types of display units and a light source of an optical communication system. By changing a luminescent material or layer structure, it is possible for the organic EL element to obtain various luminescent wave length including blue luminescence, which is difficult to obtain by a conventional inorganic EL element. Therefore, the organic EL element is widely used in the fields of various luminescent devices and color displays.
According to the basic method of manufacturing an organic EL element, it is manufactured as follows. For example, ITO film (Indium Tin Oxide), which is known as a transparent conductive film, is formed on the surface of a glass substrate so that ITO film can be used as a transparent anode. An organic thin film is laminated on this ITO film. Further, a cathode, which includes a pair electrodes together with the anode formed by ITO film, is formed on this organic thin film by means of metallic vapor deposition. Recently, a method of manufacturing an organic electroluminescence element has been adopted for the purpose of enhancing the insulating property when the cathode is formed by means of vapor deposition and also for the purpose of preventing a short circuit between the cathode and ITO film formed as an anode. The manufacturing method includes a process in which an upper end portion of an electrically insulating bulkhead provided between the organic thin film and the laminated body of the cathode and also provided between the cathodes is formed into a T-shape in the longitudinal cross-sectional shape.
The above method of manufacturing an organic electroluminescence element, in which the overhang portion is formed in the manufacturing process, is disclosed in, for example, JP-A (Japanese Unexamined Patent Publication No.) 8-315981 and others. The essential concept of the above manufacturing method is shown in FIGS. 4A-4F.
As shown in FIG. 4A, an anode is made of a transparent electrode 52 on a glass substrate 51 by means of patterning, wherein an electrically conductive transparent ITO is subjected to patterning for forming the transparent electrode 52. In this case, a plurality of rows of transparent electrodes 52 are provided in parallel to each other on a glass substrate 51 in the uniform thickness. A film of polyimide 53, which is an unphotosensitive and electrically insulating material, is formed by, for example, the method of spin coating. This film of polyimide 53 is formed on both the glass substrate 51 and the transparent electrode 52 in parallel to them in a direction perpendicular to the arranging direction of the transparent electrode 52. This film of polyimide 53 is finally formed as an insulating bulkhead. Next, as shown in FIG. 4B, an SiO2 film 54 used as material to form an overhang portion is formed by the method of spattering so that an appropriate film thickness can be obtained. After that, as shown in FIG. 4C, a photoresist pattern 55 is formed by the method of photolithography on the SiO2 film 54.
Further, as shown in FIG. 4D, the SiO2 film 54 is etched so as to be the same pattern as that of the photoresist pattern 55 while the photoresist pattern 55 is used as a mask in the process of etching. Next, as shown in FIG. 4E, the film of polyimide 53 is vertically etched by the method of reactive etching in which O2 is used as an etching gas. Then, as shown in FIG. 4F, the sides of polyimide 53 are equally subjected to side etching by the method of wet etching in which an alkali solution is used. Due to the foregoing, the overhang portion can be formed, in which the SiO2 film 54 protrudes to the transverse direction from the sides of polyimide 53.
After the process in which the overhang portion is formed, an organic thin film is formed on the upper surface of the transparent electrode 52. Further, a cathode is formed on this organic thin film by the method of vapor deposition. In the process of vapor deposition of the cathode, metallic vapor is incident upon the glass substrate 51 from above, so that metallic vapor can not come round to the side of the transparent electrode 52 and a short circuit of the transparent electrode 52 with the cathode formed by vapor deposition can be prevented.
However, according to the manufacturing method described above, the SiO2 film 54 must be etched and then polyimide 53 must be successively etched in the process until the overhang portion is formed. Even after the above two etching processes, an etching process is required in which polyimide 53 is etched in an alkaline solution. Accordingly, it is necessary to conduct the etching processes three times in total. Even if polyimide 53 is subjected to wet etching in an alkaline solution at the beginning, it is necessary to go through two etching processes, which affect the yield of products. Since the SiO2 film 54 in which plastic deformation tends to occur is formed on polyimide 53 in which elastic deformation tends to occur and the thickness of which is relatively large, cracks are easily caused in the SiO2 film 54 by the influence of heat, and there is a possibility that the reliability is deteriorated.
As described above, when the conventional organic EL element is manufactured, it is necessary to conduct etching at least twice in the process until the overhang portion is formed so that the anode made of ITO formed on the glass substrate can not be short-circuited with the cathode. Therefore, the working process becomes complicated and the productivity is affected. Since hard SiO2 is formed on soft polyimide, cracks tend to be caused on the SiO2 film 54, and the reliability is deteriorated.
JP-A No. 8-315981 discloses a manufacturing method in which a reversely tapered portion is formed by resist. However, it is impossible in principle to form a reversely tapered portion with the positive type resist. When negative type resist is used, it is easy to form a reversely tapered portion. However, it is impossible to form an acute angle in the gate portion. Therefore, metallic vapor must be incident upon the substrate after the formation of the cathode. Accordingly, various devices are required, which reduce the yield of products. When resist for image rehearsal, for example, AZ5214, which is the brand name of Hekisuto K.K., is used, it is easily possible to form a bulkhead, the taper angle of which is small. However, it has poor adhesion to the substrate, and further the profile is greatly affected by the exposure and development. Therefore, it is impossible to form a reversely tapered portion while the yield of products is maintained high.
It is an object of the present invention to provide an organic EL element, the structure of which is simple, the manufacturing cost of which is low, and the reliability of which is high. It is another object of the present invention to provide a method of manufacturing the organic EL element. It is still another object of the present invention to optimize an image generation on a display on which the organic EL element is used.
The present invention provides an organic electroluminescence element comprising: a first electrode provided on a substrate; an insulating bulkhead from which a portion of the first electrode is exposed, the insulating bulkhead being formed into a thickness so that the insulating bulkhead can be protruded to the above of the first electrode; an organic thin film formed on the first electrode and the bulkhead; and a second electrode formed on the organic thin film, wherein an overhang portion is formed at an upper end of the insulating bulkhead by a resist film used for etching the bulkhead in accordance with a region in which the organic thin film is formed.
Due to the above structure, when the resist film is left as it is and formed into an overhang portion, it is possible to provide an electroluminescence element, the lamination structure with respect to the substrate of which is simple. One of first electrode and second electrode should be made of a transparent material. In the case that the first electrode is made of transparent material, the substrate should be also made of a transparent material.
Also, the present invention provides a method of manufacturing an organic electroluminescence element comprising the steps of: forming a first electrode on a substrate; forming an insulating bulkhead from which a portion of the first electrode is exposed, the insulating bulkhead being formed into a thickness so that the insulating bulkhead can be protruded to the above of the first electrode; and forming a resist film at an upper end of the insulating bulkhead, the resist film being used for etching the bulkhead in accordance with a forming region of the organic thin film; and forming the resist film into an overhang portion with respect to the bulkhead by conducting side-etching on the insulating bulkhead.
According to the above method, only when the insulating bulkhead is subjected to side-etching so that an overhang portion can be formed while the resist film is left as it is, the organic electroluminescence element can be provided. Therefore, the number of the process required for the manufacture of the organic EL element can be reduced.